(a) Field of the Invention
The present invention relates to melt-spun synthetic fibers with formation of unique pattern of wrinkles or ridges and recesses in their surfaces, and also to a method of producing such synthetic fibers, and more particularly it pertains to synthetic fibers having surface configurations resembling those of human hair, and also to a novel method of imparting the synthetic fibers such surface conditions.
(b) Description of the Prior Art
Those synthetic fibers now being used as the materials of artificial hair for wigs include fibers of the vinyl chloride family and fibers of the acryl family. However, the synthetic fibers of these families, in general, lack resistivity to heat. Therefore, while these synthetic fibers can be relatively easily set with heat, they have a poor holdability of the imparted shape, and accordingly, they have problems in, for example, shampooing with warm water and in drying by means of hair-dryers. On the other hand, those synthetic fibers which are obtained by the melt-spinning process have sufficient resistivity to heat, but, owing to the fact that these synthetic fibers have very smooth surfaces, they present specular luster peculiar to them and give a unique waxy sense, and thus their user cannot help getting dissatisfied with both the feel and the sense of touch of these fibers as they are used for wig hair, and accordingly these synthetic fibers must be said to be far from human hair in property and quality.
There have been reported in the past various methods of supressing and reducing the luster of those synthetic fibers which are obtained by melt-spinning. For the purpose of doing so, there has been widely known technique of introducing an inorganic substance such as silica or titanium oxide in the starting material synthetic resin before being subjected to melt-spinning. While this method is effective in depriving the produced synthetic fibers of their luster, still it is not desirable since the fibers' color-expression is adversely affected.
Japanese Patent Preliminary Publication No. Sho 48-13695 discloses a method of supressing the reflection of light at the surface of the thus-spun synthetic fibers by covering the fiber surfaces with a resin having a low refractive index. Nevertheless, the smoothness of their surfaces are not reduced, and the fibers are substantially short of the sense of touch and feel of human hair.
Various attempts have been developed so far to improve the specular luster of these fibers by causing random or irregular reflection of light by developing uneven pattern in the surface of fibers to thereby improve the feel and sense of touch. For example, Japanese Patent Publication No. Sho 43-22349 discloses a method of subjecting the surface of the polyamide fiber to dissolution or erosion with an inorganic acid. Japanese Patent Preliminary Publication Nos. Sho 55-107512 and Sho 58-163719 both disclose methods which are to uniformly diffuse fine particles of an inorganic substance in polyester, and after melt-spinning of same, the surface of the resulting filament is subjected to etching with a solvent or an alkaline solution to thereby form an uneven surface. However, such chemical erosion process is intended to develop an uneven surface configuration by developing erosion holes in the surface of the already-made (commercially available) fiber. Accordingly, these fibers are poor in the scratchy sense of the human hair provided by fine projections which the human hair possesses throughout its surface, and also these fibers mentioned above are not suitable for use as the artificial hair to be used in making wigs.
Apart from the above, as a physical surface-reforming technique, Japanese Patent Publication No. Sho 59-11709, for example, discloses a method of imparting a polyester fiber an uneven surface by subjecting the surface to the irradiation of glow-discharge plasma. This method, however, brings about a rise in the production cost, so that it is not appropriate for the production of artificial hair for wigs.